New insights into the genetic loci related to egg weight and age at first egg traits in broiler breeder

Egg weight (EW) and age at first egg (AFE) are economically important traits in breeder chicken production. The genetic basis of these traits, however, is far from understood, especially for broiler breeders. In this study, genetic parameter estimation, genome-wide association analysis, meta-analysis, and selective sweep analysis were carried out to identify genetic loci associated with EW and AFE in 6,842 broiler breeders. The study found that the heritability of EW ranged from 0.42 to 0.44, while the heritability of AFE was estimated at 0.33 in the maternal line. Meta-analysis and selective sweep analysis identified two colocalized regions on GGA4 that significantly influenced EW at 32 wk (EW32W) and at 43 wk (EW43W) with both paternal and maternal lines. The genes AR, YIPF6, and STARD8 were located within the significant region (GGA4: 366.86-575.50 kb), potentially affecting EW through the regulation of follicle development, cell proliferation, and lipid transfer etc. The promising genes LCORL and NCAPG were positioned within the significant region (GGA4:75.35-75.42 Mb), potentially influencing EW through pleiotropic effects on growth and development. Additionally, 3 significant regions were associated with AFE on chromosomes GGA7, GGA19, and GGA27. All of these factors affected the AFE by influencing ovarian development. In our study, the genomic information from both paternal and maternal lines was used to identify genetic regions associated with EW and AFE. Two genomic regions and eight genes were identified as the most likely candidates affecting EW and AFE. These findings contribute to a better understanding of the genetic basis of egg production traits in broiler breeders and provide new insights into future technology development.

Polymorphism, Genetic Effect, and Association with Egg-Laying Performance of Chahua Chickens Matrix Metalloproteinases 13 Promoter

Matrix metalloproteinases are a group of proteases involved in the regulation of ovarian follicular development and ovulation. Among the different MMPs, MMP13 is known to play an important role in reproduction. Therefore, this study aimed to screen the molecular genetic markers of the MMP13 gene that affect the egg-laying performance of Chahua chickens. Polymerase chain reaction (PCR) and sequencing were performed in the 5' regulation region of the MMP13 gene to detect loci significantly related to the egg-laying performance of Chahua chickens. A double fluorescence reporting system, quantitative reverse transcription PCR (RT-qPCR), and Western blotting were used to study whether gene expression was regulated by identified sites, providing a theoretical basis to improve egg production in Chahua chickens. The results revealed six single nucleotide polymorphisms (SNPs; A-1887T, T-1889C, A-1890T, T-2252C, T-2329C, and C-2360A) in the promoter region of the MMP13 gene. Further analysis revealed that hens with T^-1890-C^-1889-T^-1887/T^-1890-C^-1889-T^-1887 (mutant type, MT) had an earlier age at first egg (AFE) than hens with A^-1890-T^-1889-A^-1887/A^-1890-T^-1889-A^-1887 (wild type, WT; p < 0.05). RT-qPCR showed that the relative expression level of the MMP13 gene in the ovarian tissues of individuals with the mutation was higher than that of individuals with the wild gene (p < 0.05). Western blot results confirmed higher levels of the MMP13 protein in MT ovaries compared to those in WT ovaries. Thus, this study suggests that mutation sites on the MMP13 promoter may affect gene expression. In conclusion, the MMP13 gene in Chahua chickens may be significant for egg-laying performance, and the polymorphism in its promoter region could be used as a molecular marker to improve egg-laying performance.

Effect of age at first egg on reproduction performance and characterization of the hypothalamo-pituitary-gonadal axis in chickens

As an important indicator of sexual maturity of hens, age at first egg (AFE) is significantly associated with reproduction performance. In this study, 400 hens were divided into 6 groups based on AFE to analyze the difference of reproduction performance, reproduction hormone levels and the characterization of the hypothalamo-pituitary-gonadal axis in chickens. The results showed that the egg production of the hens in the late-maturing groups was significantly lower than that of the ones in other groups and the precocious hens had a lower egg production rate. The hens in late-maturing group had a lower fertility rate, LH levels and shorter duration of peak of egg production (PEP), the precocious hens had lower PRL levels. In addition, the characterization of the hypothalamo-pituitary-gonadal axis showed that the individuals with normal AFE had higher GNRH, GNRHR, ESR1, KITLG, and CYP11A1 expression levels than late-maturing and precocious individuals, which indicated that the chickens with normal AFE advantages on reproduction regulation system.

Using random regression models to estimate genetic variation in growth pattern and its association with sexual maturity of Thai native chickens

1. Genetic (co)variances and parameters between body weights (BW) across the growth trajectory were estimated using a univariate random regression (RR) animal model. The effect of growth rates (GH) on age at first egg (AFE) and egg weight at first egg (EWFE) were explored using a series of univariate and bivariate analyses. 2. Body weights were taken from Thai native chickens at hatch day to 168 days of age. The model included interactions between age with hatch nested within year and sex as fixed effects, and random effects of direct additive genetic, direct permanent environmental, maternal genetic and maternal permanent environmental effects. All random effects were fitted as regressions to animals' age via quadratic Legendre polynomials and fitting six classes of residual variances was identified as an optimal variance structure to estimate parameters. 3. Genetic and phenotypic variances for BW increased with increasing age. Estimated heritabilities for direct additive (h² _a) and maternal genetic (h² _m) effects on BW traits ranged from 0.34 to 0.54, and 0.04 to 0.06, respectively. Estimated variance ratios for direct (c² _ape) and maternal permanent environmental (c² _mpe) effects ranged from 0.19 to 0.48 and 0.10 to 0.12, respectively. Estimated correlations between weights at different ages were high for all random effects. 4. Estimated h² _a for six GH traits ranged from 0.06 to 0.28, while for AFE and EWFE these were 0.24 and 0.16, respectively. Estimated h² _m and c² _mpe were low for GH. Estimated genetic correlations between GH and AFE ranged from -0.22 to 0.02 and, between GH and EWFE, ranged from -0.05 to 0.40. These estimates suggested that selecting high GH chickens at 28 days of age can be expected to reduce AFE and to increase EWFE.

Genetic parameters for clutch and broodiness traits in turkeys (Meleagris Gallopavo) and their relationship with body weight and egg production

The objective of this study was to estimate phenotypic and genetic parameters for clutch and broodiness (BR) traits in turkeys and their relationship with body weight and egg production. Data on dam line hens was available and included: body weight at 18 wk of age (BW18), body weight at lighting (BWL, 29 to 33 wk), age at first egg (AFE), egg number (EN), rate of lay (RL), clutch length (CL), maximum clutch length (MCL), pause length (PL), maximum PL (MPL) and BR. BR was defined as the average number of consecutive pause days between clutches that was higher than the average PL per hen. Heritability estimates for BW18 and BWL were 0.50 and 0.53, respectively. The heritability for egg production, clutch, and pause traits varied from low (MPL = 0.15; BR = 0.15) to moderate (AFE = 0.22; EN = 0.28; RL = 0.29; CL = 0.21; MCL = 0.27; PL = 0.25). Genetic correlations were negative between body weight traits and EN (r_{g (BW18, EN)} = −0.27; r_{g(BWL, EN)} = −0.33) and CL (r_{g(BW18, CL)} = −0.40; r_{g(BWL, CL)} = −0.33). BR was negatively genetically correlated with EN (r_{g(BR, EN)} = −0.85) and CL (r_{g(BR, CL)} = −0.30), and positively genetically correlated with PL (r_{g(BR, PL)} = 0.93) and AFE (r_{g(BR, AFE)} = 0.21). EN had a positive (0.73) and a negative (−0.84) genetic correlation with CL and PL, respectively. Overall, the results of this study confirmed the negative (unfavorable) correlations between egg production and body weight. Despite unfavorable genetic and phenotypic correlations between egg production traits and those relating to BR, the inclusion of BR in a selection program through incorporation of clutch length traits and pause length traits is feasible. Integration of either clutch length traits or pause length traits in a selection index is likely to increase egg number while decreasing broodiness.